1. Field of the Invention
The present invention relates to an optical signal delay module and a method thereof, particularly to a module and method, which reversely feedbacks an amplified spontaneous emission generated by an optical amplifier to the optical amplifier through a loop to modify the group refractive index of the amplifier. By varying the group refractive index of the optical amplifier, the transmission of optical signals can be delayed.
2. Description of the Related Art
Fiber-optic communication is a communication method based on light and optical fibers. Light can be used to carry information after being modulated where it features a superior transmission capacity and a high information security. Since 1980s, the fiber-optic communication system plays a very important role in the digital world. In principle, the outgoing information is transferred from the sender side to the transmitter, and the signal modulates the carrier wave, which functions as the transmission medium of information, and then the modulated carrier wave is sent to the recipient side in a distant place, and the receiver demodulates the modulated carrier wave to obtain the original information.
A single optical fiber can simultaneously transfer several groups of signals having different wavelengths, such as the signals of telephone, the Internet, and cable TV. Optical fiber outperforms copper wire in signal impairment and signal interference, and the advantages are especially obvious in long-distance massive data transmission. After different-wavelength optical signals are coupled and sent into the incident side, the different-wavelength optical signals will have different phase delays inside the waveguide because different-path signals have different timings. Thus, the data traffic may exceed the processing capability of the recipient side. Therefore, the optical fiber network needs technologies to delay optical signals and guarantee that data traffic is within the processing capability of the recipient side to prevent data loss. The current optical signal delay technologies are usually based on controlling optical signal paths. However, such a design has to reserve extra optical signal paths in the optical network topology, it also requires a plurality of optoelectronic switches or mechanical switches and a complex control system, which consumes a lot of space and higher installation cost. Please refer to FIG. 1 for a proposed experimental setup by H. Su, and S. L. Chuang in Applied Physics Letters, Vol. 88, Art. No. 061102, 2006: an external pump laser is counterclockwise injected into a semiconductor optical amplifier (SOA) via an optical circulator, and the delay of optical signals can be controlled by varying the power of the pump laser. However, such a technology needs an external high-power and high-stability pump laser which is high in cost.
To overcome the abovementioned problem, the present invention proposes an optical signal delay module, which adjusts power of amplified spontaneous emission generated by a semiconductor optical amplifier (SOA) and reversely feeds the adjusted ASE back to the SOA. Thereby, the present invention can vary the group refractive index of the optical amplifier to achieve optical signal delay. Thus, the present invention, can replace the conventional pump laser required by a coherent population oscillation mechanism which greatly reduce the cost of establishing an optical network.